10-bolt or 12-bolt? Huh?

[Guest]

Was going to change the fluid in the rear axle of my 70 Electra, so I went to the NAPA store to buy a rear axle cover gasket. The guy looks in the book and asks if it's a 10-bolt or 12-bolt.<P>Well, "of course" it's a 12-bolt, I reply....thinking what else would a 4500 lb. car with a 455 use?<P>When I got the home, and crawled under the car, I was stunned to see that there are only 10 bolts on the axle cover! (and of course the gasket is wrong)<P>What's up with this? Granted, it's one huge axle, but I'm surprised to see only 10-bolts on the cover. Also, it is not the same bolt pattern as the 10-bolt on my "puny" 327 66 Caprice. <P>Can someone enlighten an ol' Chevy guy? (I'm used to 10-bolts on the "little" engines, and 12-bolts on the "big" engines)

[Guest 70 Electra]

See... I really AM a registered user. (Don't know what happened......)

[Guest]

I HAVE A '70 LESABRE CONVT W/A 350-2BBL.<BR>I HAD TO CHANGE THE REAR AND THE ONLY ONE I COULD GET MY HANDS ON WAS ONE OUT OF THAT ERA ELECTRA/WILDCAT.<BR> APP.THERE ARE TWO REARS FOR THE BIG CAR.<BR> THEY ARE BOTH 10 BOLT. THE SHOCK AND SPRING<BR>MOUNTS ARE THE SAME, THE BRAKE HARDWARE AND THE DRUMS ARE ALSO THE SAME.<BR> THE COVERS ARE DIFFERENT,I CAN'T RECALL THE DIFFERENCE RIGHT NOW.<BR> INTERNALLY THEY ARE DIFFERENT,SO AFTER I INSTALLED THE "NEW" REAR,EVERYTHING BOLTED IN, EXCEPT THE DRIVE SHAFT. THERE WAS LESS ROOM BETWEEN THE FRONT OF THE REAR END HOUSING AND THE BACK OF THE TRANS.<BR> I INSTALLED A DRIVESHAFT MARKED "CHEVY"<BR>FROM THE JUNKYARD.<BR> I THINK IT BREAKS DOWN THIS WAY: LITTLE MOTOR(350)-"LITTLE" 10 BOLT.<BR> BIG MOTOR(400/430/455)-"BIG" 10 BOLT.<BR> I THINK IF YOU HAVE A LESABRE 400-THAT <BR>INDICATES A 350 4BBL W/THE 400 TRANS AND MAYBE,MAYBE,THE "BIG" 10 BOLT.<BR> I THINK THE RIV HAS THE "BIG" 10 BOLT, BUT W/O THE "EARS" ON THE TOP OF THE HOUSING FOR MOUNTING THE UPPER CONTROL ARMS.<BR> IT'S ONE OF THOSE THINGS YOU NEVER THINK ABOUT UNTIL SOMETHING GOES WRONG...

[Guest]

The parts guy was using "Chevy talk". Chevy rearends are completely different from BOP (buick olds pontiac) rear ends. Next time just have them look it up in their book, or bring the old gasket in with you. <BR> Parts people are usually pretty dense so you need to specify BOP rear-end.

[Guest]

What you have is a 9 3/8<BR>rear end.This was used in electra/wildcat/estate wagon/riviera and the Lesabre 455 model.The Lesabre 350 rear is 8 1/2 inch.Same internals as the GS.<BR>Many parts places give the 8 1/2 rear cover<BR>gasket as the one needed.<BR>The 9 3/8 is more square in appearance.

[NTX5467]

The other alternative to rear axle fluid changes is to use a suction gun, just like the service station people used to use. Not all rear axles have removeable "inspection covers" so that's the only way to get the fluid out. An example would be the Chrysler 8 3/4 rear axle where the back surface is smooth with only a screw-in plug.<P>The B-O-P rear axles are completely different from the Chevy axles in all respects. There could be some applications where the whole assemblies will bolt into the same chassis, but the similarities end there. There could also be some unique items within the same axle family for certain years also.<P>With respect to Chevrolet rear axles, the number of cover bolts typically is indicative of the ring gear diameter, with the 10 bolt typically being the 8.5" ring gear diameter and the 12 bolt axles having larger ring gear diameters. Other GM axles should not be judged in the same manner, though, as the size and shape of the cover could vary with the same number of hold down bolts.<P>It could have been that the parts person "thought" all of those axles were the same so when they start asking "unusual" questions, it might mean there's some trouble in the parts database they are using or they've mistakenly keyed in for the wrong vehicle.<P>It might seem flaky, but taking the old part along could be good advice in some situations.<P>NTX5467<p>[ 07-25-2002: Message edited by: NTX5467 ]